The objectives of this project are to study the participation of the contractile protein system in blood platelet function. The studies to be conducted will be concerned with the mechanism(s) by which actomyosin, under the effect of aggregating agents, activates and/or inhibits contraction, relaxation, secretion and aggregation. The interaction of each of these elements with contractile proteins will be studied in order to determine how they initiate, maintain and suppress each of the physiological functions of platelets that control normal hemostasis. Clarification of the spatial arrangement of the different proteins that constitute the contractile protein at the platelet membrane should improve our understanding of the role of microfilaments in platelet function. With the aid of antibodies directed toward specific fragments of the contractile proteins it should be possible to monitor the relation between these proteins and aggregation, secretion and the role of platelets in the formation of arteriosclerotic plaques. c-AMP levels, suggested to play a key role in aggregation, may be linked to Ca2 ion mobilization; therefore, studies will be carried out on the phosphorylation of a protein from sarcoplasmic reticulum, and the involvement of c-AMP on the catalysis of this reaction and the influence on the sequestration of Ca2 ion by the microscomes. The lower ATPase activity of platelet actomyosin, as compared to muscle, may be due to a missing light chain on the myosin molecule. Therefore, isolation, characterization and hybridization experiments are necessary to understand their biological functions. BIBLIOGRAPHIC REFERENCE: Puszkin, E.G., Spaet, T.H., Zucker, M.B. Platelet Rod-Myosin and effect of antibodies on platelet aggregation, release and clot retraction. Blood 46:1031, 1975.